As the cushioning material for household articles, beds, railway vehicles, automobiles, etc., usually used at the present time are urethane foam, non-elastic crimped fiber battings, and resin-bonded or hardened fabrics made of non-elastic crimped fibers.
Urethane foam, although it has excellent durability as a cushioning material, has the following disadvantages. First, urethane foam exhibits high excess compressibility and high stuffiness because it has not only poor permeability both to water vapor and to water but also regenerative properties. The addition of a halide is necessary for giving flame retardant properties to urethane foam because a great quantity of heat is evolved at the combustion, which causes a problem that poisoning may be caused by toxic gases evolved in great volume when a fire breaks out. Because the recycling of urethane foam is difficult, waste urethane foam is incinerated, in which case the incinerator is severely damaged and the removal of toxic gases costs a great deal. For this reason, waste urethane foam is mostly buried in the ground, which causes several problems that the ground for burying may be restricted to specific places because the stabilization of a ground is difficult and that the cost of burying may be gradually raised. Further, urethane foam, although it has excellent processability, has a disadvantage that chemicals used in the production thereof may cause environmental pollution.
In the polyester fiber batting, the fibers are not fixed with each other, and therefore, the batting obtained has a problem that it may exhibit a decrease both in bulkiness and in resilience because of its shape breaking during the use, fiber movement and plastic deformation of fiber crimps.
Some examples of the resin-bonded fabric using polyester fibers bonded together with an adhesive such as a rubber-based adhesive are disclosed in JP-A 60-11352 (1985), JP-A 61-141388 (1986) and JP-A 61-141391 (1986). An example of the resin-bonded fabric using urethane is disclosed in JP-A 61-137732 (1986). These cushioning materials have disadvantages that they had poor durability, that they cannot be recycled and that complicated procedures are necessary for their processing. They also have a problem that environmental pollution may be caused by chemicals used in the production thereof.
Some examples of the hardened fabric using polyester fibers are disclosed in JP-A 58-31150 (1983), JP-A 2-154050 (1990) and JP-A 3-220354 (1991). Because the bonding-component of heat-bonding fibers used is a brittle amorphous polymer (see, e.g., JP-A 58-136828 (1983), JP-A 3-249213 (1991)), the bonded portions of the fibers are also brittle, and they can easily be broken during the use, so that the fabric changes its shape and has decreased resilience, which further brings about a decrease in durability.
As a modification, there is an interlocking treatment of constituent fibers proposed in JP-A 4-245965 (1992). Even with this treatment, the bonded portions of the fibers remain brittle and the resilience is, therefore, significantly decreased. In addition, complicated procedures are necessary for the processing of a material obtained. Further, there is a problem that the bonded portions of the fibers can hardly change their shapes and it therefore makes difficult to obtain a cushioning material having softness.
For this reason, a heat-bonding fiber using a soft polyester elastomer capable of recovering its original shape, even if given deformation, is proposed in JP-A 4-240219 (1992), and a cushioning material using this fiber is proposed in WO 91/19032 (1991). If the bonding component used in this structured fiber material is restricted to a polyester elastomer containing terephthalic acid in a proportion of 50 to 80 mol %, as an acid monomer for the hard segment and polyalkylene glycol in a proportion of 30% to 50% by weight, as a glycol monomer for the soft segment, an additional acid monomer to provide a polyester elastomer having a melting point below 180.degree. C., which seems to be the same as the case of a fiber as disclosed in JP-B 60-1404 (1985), can be considered as isophthalic acid. The polyester elastomer therefore becomes more amorphous, and the bonded portions of the fibers can readily be formed into an amoebic shape because of its low melting viscosity. The material obtained is, however, liable to cause plastic deformation, and when it is used as a cushioning material, there is a problem that the resistance to compression at high temperatures may be decreased. Accordingly, the material cannot find any application requiring resistance to plastic deformation at high temperatures.